Formed wafers are curved laminates often produced as an intermediate step to a completed lens. For example, a wafer may be produced having a delicate functional layer, such as a polarizing or photochromic layer, sandwiched by a first, protective layer and a second, base layer. The wafer is then formed to have a base curve. The formed wafer is then placed in an injection mold chamber where a molten lens material is injected behind the wafer to form a lens against the base layer of the wafer. In the alternative, the formed wafer can be used simply as a piano lens by itself, e.g., as a plano polarized or photochromic sunglass lens or sungoggle, i.e., without injecting a molten lens material behind the wafer. An example of such a wafer is disclosed in publication EP 0 299 509 A2 by Kawaki et al., incorporated by reference herein in its entirety.
The wafers are typically formed via a process that includes first heating the polymeric wafer to a softening temperature. This heating step may be accomplished in a variety of ways such as with hot air or heated forming molds. Next the softened wafer is placed in a forming cup and either pressed or sucked into the forming cup. The wafer is held in the cup until it sets, thus assuming the shape of the forming cup. The wafer is then removed and cooled to ambient temperature.
Typical heating or softening temperatures for use in forming the laminated wafer are determined by the thermal properties of the materials chosen for producing the laminated wafer. One example of materials that have been previously used in making laminated wafers is polycarbonate resin films or sheets. Polycarbonate films or sheets include general aromatic polycarbonate resin sheets prepared from bisphenols (e.g., bisphenol A) and phosgene or carbonic esters and sheets prepared from transparent copolycarbonate resins or transparent resin compositions containing other resins. If desired, these polycarbonate sheets may thereafter be coated or otherwise treated with a functional coating, such as heat-formable hard coat, an anti-fogging coat, an infrared-reflective or infrared-absorbable coat, an ultra-violet reflective or ultra-violet absorbable coat or other similar functional coatings that are known in the art.
Other materials contemplated for use in making laminated wafers may include adhesives or functional materials such as polarizing films or photochromic films. Examples of adhesives that are contemplated for use in laminated wafers may include PVA adhesives or urethane adhesives that are commonly known in the polycarbonate lens industry. Examples of a polarizing film suitable for use in laminated wafers include a polarizing film containing components such as polyvinyl alcohol polymer (PVA) film, which is monoaxially stretched before dyeing, or dyed before monoaxial stretching, and subjected to fixing treatment with a boron compound (in some cases, the dyeing and fixing treatment are conducted simultaneously). Other examples of functional materials may include polyester polarizers or photochromic polarizing films.
Once the functional layer, such as a polarizing PVA film, has been incorporated, then a protective film having optical transparency and mechanical strength is normally laminated on each surface or one surface thereof. Examples of protective layer materials would typically include materials such as cellulose tri-acetate (CTA) film, cellulose acetate butyrate (CAB) and other cellulose resins, cyclic olefin, polyesters, such as polyethylenetelephthalate (PET) and its alloy or modified resin, polycarbonate alloy and copolymer with other polymer(s), polyethylenenaphthalate (PEN), and acrylic resins, such as polymethyl methacrylate (PMMA).
Laminated wafers having the above-described materials are thereafter formed into curved laminates. This process is commonly accomplished using a machine, such as those made by Lema of Italy. The Lema machines have a thermostatically-controlled electric heating chamber with an air blower, and forming cups mounted on a rotating turret. A vacuum hole at the bottom of each forming cup allows the wafers to be sucked into the cups and held in place with a vacuum. Vacuum control valves hold the wafers until they reach a designated position on the rotating turret at which time they are released.
Other machines that are suitable for use in making laminated wafers are produced by Japanese companies such as Wintec and Fuji Kasei. These are similar to the Lema machine but also include wafer pre-heating units, pick and place mechanisms, and plungers to mechanically press the wafers into the vacuum cups. Some machines also have a cooling conveyor or other apparatus used to achieve desired formation(s) of selected wafer components.
These machines perform adequately when forming a wafer that has a protective layer and a base layer having similar properties and/or materials. However, they are found to be deficient to form wafers where the protective layer is different than its base layer. Materials having similar properties, such as softening properties, can be heated and formed uniformly at a uniform temperature. For example, the softening temperature of a laminated wafer having a protective layer and a base layer comprised entirely of polycarbonate materials, or similar-propertied materials, is at or near approximately 285° F. Therefore, placing the laminated wafer in a heated environment possessing a uniform temperature of approximately 285° F. over a prescribed amount of time will result in a softening and formation of a uniformly curved laminated wafer, appropriate for use thereafter in a manufacturing process, such as injection molding. However, preparing a laminated wafer where one or more layers have properties and/or materials that are different from other layers, and exposing such a wafer to a uniform heat that is outside a prescribed or required softening temperature for one of the materials will result either in inadequate softening and forming (e.g. when the temperature is too low) or, alternatively, a softening of the material to a point of damaging the material (e.g. when the temperature is too high).
One example of a laminated wafer having different layer materials is a wafer having a CAB film as a protective layer, a PVA film as a polarizer functional layer, and a polycarbonate film as a base layer. The optimum softening and forming temperature for the polycarbonate film base layer occurs at or near 285° F. At temperatures substantially below this temperature (e.g. t 270° F. or below), polycarbonate does not undergo adequate softening due to its chemical and structural properties, namely its thermal properties. Alternatively, at temperatures above 260° F., CAB becomes too soft because the temperature is too high to maintain the chemical and structural integrity of the material due to its underlying thermal properties. Thus, the aforementioned machines are unable to form a wafer including, for example, a CAB film protective layer and a polycarbonate film base layer because there is no operational temperature window that satisfies both layers.
There is thus a need for a machine that is able to soften and form laminated wafers having different layers of materials with diverse thermal properties.